1. Field of the Invention
The present invention relates to a method and apparatus for inspecting an inspection object for airtightness failure using a leak inspecting medium (tracer gas) such as helium gas.
2. Description of the Related Art
As one of prior art inspection methods used for detecting a minute airtightness failure of an inspection object, there exists an inspection method using a helium leak detector (a helium leak detecting device) for detecting an amount of tracer gas leaking from the inspection object. In this type of inspection method, there are two methods, as shown in FIGS. 4A and 4B, and they are a vacuum-type helium leak inspection method and a sniffer-type helium leak inspection method.
As shown in FIG. 4A, the vacuum-type method is a method in which an inspection object 1 is accommodated within a vacuum container 2 which has been evacuated with an evacuating pump 3, helium, which is a tracer gas, is sealed in the inspection object 1 under pressure, and helium leaking from the inspection object 1 into the vacuum container 2 is introduced into a detector (a helium detector) for detection making use of the mass analysis of helium. Note that reference numeral 5 denotes an evacuating pump for the detector 4, and reference numeral 6 denotes a controller for controlling valves and for gathering data.
However, in the event that a minute leak must be detected at high speed and with high accuracy using this method, the detector 4 must be connected to the vacuum container 2 for detection after the inspection object 1 is installed in the vacuum container 2 and the periphery of the inspection object, that is, the interior of the vacuum container 2, is made a vacuum. In addition, the interior of the vacuum container 2 has to be finished so that the interior surface of the vacuum container 2 can provide little profile irregularity in order to reduce a risk of the adsorption of helium to a lowest level.
In addition, in the event that an object is inspected with this method which is large in size and complicated in configuration, the vacuum container 2 also needs to be enlarged, this leading to a problem that a tremendous amount of labor and cost is involved in maintaining its required durability and low profile irregularity. In addition, in order to reduce the inspection time, a vacuum needs to be drawn within the vacuum container 2 having a large capacity within as short a period of time as possible, which in turn requires a high-performance evacuating pump for creating the vacuum, resulting in the problem of the production costs being increased further.
Furthermore, there exists a further problem with the utilization of this vacuum-type method that the shape of the inspection object 1 is limited to those which can be installed in the vacuum container 2.
On the other hand, the sniffer-type helium leak detecting method, which is the other prior art method, is a method in which an inspection object 1, in which helium is sealed under pressure, is left exposed to the atmosphere, and a sniffer probe 7 connected to a detector (a helium leak detector) 4xe2x80x2 is brought into abutment with the external surface of the inspection object 1 to be traversed around the surface for detecting a leakage of helium gas from the interior of the inspection object. Note that reference numeral 5xe2x80x2 denotes an evacuating pump for evacuating the detector 4xe2x80x2, and reference numeral 6xe2x80x2 denotes an external device for gathering data.
While it is an effective method for detecting leak positions and rough leak amounts of helium gas leaking from the inspection object 1, this sniffer-type method has a problem in that, with this method, it is difficult to realize the quantification of leak amounts and detection with high accuracy.
In addition, in the event that there exist intermediate portions along the length of a path along which the sniffer probe is moved, where walls, pipes and wires are arranged in a complicated fashion, the sniffer probe cannot reach the vicinity of an inspecting position of the inspection object, and therefore, an accurate inspection is not possible. There is known a leak detector which is disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2001-228045 as a solution to the aforesaid problem. In this leak detector, a sniffer probe inlet port is designed to be detachably attached to a position near an inspecting location of an inspection object using an attaching means. Even with this apparatus, however, although the position where a leak occurs can be identified relatively accurately, the quantification of leak amount and highly accurate detection cannot be attained.
The present invention was made in view of the above problems, and an object thereof is to realize the following at one time:
(1) To reduce inspection costs for inspecting a small-sized inspection object or a limited inspection area of even a relatively large-sized inspection object for a minute airtightness failure;
(2) To enable the inspection of a relatively large-sized or complicatedly shaped inspection object in the atmosphere without installing the entirety of the inspection object;
(3) To realize the quantification of a leak and the detection of leak with high accuracy even in the atmosphere, which is not possible with the prior art sniffer-type helium detector; and
(4) To relax the restrictions on inspection objects in inspecting for airtightness failure.
According to an aspect of the invention, there is provided a method, for inspecting for airtightness failure, comprising an initial step of generating an independent constant flow of gas in a cover formed in such a manner as to surround an inspecting area of an inspection object and a detector, respectively, a pre-inspection step of sealing a tracer gas in the inspection object under pressure and placing the cover over the inspecting area, a measuring step of introducing a gas including the tracer gas leaking from the inspection object and drawn out of the cover into the detector for measuring the amount of a leak, and a cleaning step of cleaning flow paths constituting flow path systems of the gas and instruments including the detector after the measuring. This enables the inspection of an inspection object in the atmosphere without installing the entirety of the inspection object in a vacuum container and the realization of quantification of the amount of a leakage and detection of a leakage with high accuracy.
According to another aspect of the invention, there is provided a method, as set forth in the initial aspect of the invention, wherein the constant flow of gas flowing in the cover and the other constant flow of gas flowing in the detector at the initial step are adjusted so as to have the same flow rate. This enables further the realization of quantification of the amount of a leakage and detection of a leakage with high accuracy.
According to a further aspect of the invention, there is provided a method as set forth in the initial aspect of the invention, wherein the cleaning step of cleaning the flow paths constituting the flow path system of the gas and the instruments including the detector includes three modes, whereby the entirety of the flow paths and the device can be cleaned up completely so that no tracer gas is allowed to remain in the cover, the flow paths and the instruments including the detector, thereby enabling measurement with high accuracy.
According to an aspect of the invention, there is provided a method as set forth in the initial aspect of the invention wherein, in case the constituent of the tracer gas exists in the atmosphere, the measurement is implemented by calculating of a difference between an output when there occurs no leakage and an output when there occurs a leakage. This reduces the influence of a change in the amount of the constituent in the atmosphere.
An airtightness failure detector according to the invention is an apparatus for carrying out the airtightness failure detecting method according to the initial aspect of the invention and has first and second gas flow path systems, a test flow path system and a cleaning flow path system.
The present invention may be more fully understood from the description of preferred embodiments of the invention, as set forth below, together with the accompanying drawings.